The present invention is directed to improved fibrous absorbent structures having separate layers (or strata) as regions for fluid acquisition, storage, and distribution. The structures are useful in providing improved disposable absorbent products, such as diapers, adult incontinence pads, and sanitary napkins.
Absorbent articles such as disposable diapers, adult incontinence pads, sanitary napkins, and the like, are generally provided with an absorbent core or storage layer, to receive and retain bodily liquids. The absorbent core is usually sandwiched between a liquid previous top sheet, whose function is to allow the passage of fluid to the core, and a liquid impervious backsheet which contains the fluid and prevents it from passing through the absorbent article. An absorbent core (e.g., for diapers and adult incontinence pads) typically includes fibrous batts or webs constructed of defiberized, loose, fluffed, hydrophilic, cellulosic fibers. The core may also include superabsorbent polymer (SAP) particles, granules, flakes or fibers. In addition, an absorbent article may contain a distribution layer that aids in transporting liquid quickly from the acquisition layer to the storage layer of the core. Conventional absorbent products have used separately formed layers for acquisition, distribution, and storage leading to complex and crowded production lines. A need, therefore, exists for an absorbent product where the acquisition, distribution, and storage functions are all performed in a single integrated structure.
Market demand for thinner and more comfortable absorbent articles has increased. Such articles may be obtained by decreasing the thickness of the diaper core, by reducing the amount of fibrous material used in the core while increasing the amount of SAP particles, and by calendering or compressing the core to reduce caliper and hence, increase density. However, higher density cores do not absorb liquid as rapidly as lower density cores because densification of the core results in smaller effective pore size. Accordingly, to maintain a suitable liquid absorption rate, it is necessary to provide a lower density layer having a larger pore size above the high density absorbent core to increase the rate of acquisition of liquid discharged onto the absorbent article. Because of the inadequate pore sizes, traditional absorbent structures have suffered from an inability to absorb large surges of fluid. A need clearly exists for absorbent structures having an acquisition layer of sufficient pore size to better accommodate fluid surges.
In a conventional multilayer absorbent structure having an acquisition layer, a distribution layer and a storage layer, the acquisition layer acquires the liquid insult and quickly transmits it by capillary action away from the skin of the wearer (in the Z-direction). Next, the fluid encounters the distribution layer. The distribution layer is typically of a higher density material, and causes the liquid to migrate away from the skin of the wearer (in the Z-direction) and also laterally across the structure (in the X-Y directions). Finally, the liquid migrates into the storage layer. The storage layer generally includes high density cellulosic fibers and SAP particles. The liquid is absorbed by the storage layer and especially the SAP particles contained therein.
Although the conventional multilayer structure described above can be effective, one disadvantage of this arrangement is that because the distribution layer is on the side of the storage layer facing the skin of the wearer, there is a possibility that liquid can pool against the skin of the wearer before it is absorbed by the storage layer due to relatively poor fluid retention of the distribution layer. As the wearer moves, pressure is created and can result in fluid being released, thereby rewetting the wearer. Accordingly, it would be desirable to provide a structure wherein liquid is immediately acquired and transmitted away from the skin of the wearer in the Z-direction; where it can be absorbed into the storage layer while minimizing or eliminating the problem of liquid recontacting the skin of the wearer.
The present invention provides a unitary absorbent structure including a fluid acquisition stratum; a fluid distribution stratum; and a fluid storage stratum between the acquisition stratum and the distribution stratum. Each of the acquisition, distribution, and storage strata are in fluid communication with each other.